Gramophone pick-up



y L 1930- w. MURKHAM 1,769,532

GRAMOPHOI IE PICK-UP Filed March 15, 1929 Patented July 1, 1 930 UNITED STATES LEONARD wan'rna musician, or LONDON, ant-am GRAMOPHONE PICK-UP Application filed March 15, 1929, Serial No. 347,894, and in Great Britain latch 15, 1928.

The invention relates to electro-magnetic devices for transforming vibrations .to electrical currents of similar frequencies, and in particular to instrumentsfor obtaining electrical reproduction of sound records.

The present invention comprises a device for transforming vibrations into an alternating electric current, consisting of a permanent magnet system in the field of which is freely supported an armature which also passes through an electric coil in the alternating current circuit and is connected to stylus or equivalent vibrator.

The device may contain two oppositely I5 disposed permanent magnets of the U-shaped type, the armature bemg supported in an air gap formed between the oppositely disposed poles ofthe two magnets. The electric coil is preferabl supported in the magnetic field between t e arms of the U-shaped permanent magnet, and when two magnets are used the same coil extends between the arms of both magnets.

In the preferred construction of the device the armature extends through the coil axially' and is'su ported at itsfend on side membef's connecte to a i'vot bar'which also carries the member hol in the stylus or equivalent vibrator. The si emembers may be mounted on a damped by rub er.

A manner of carrying out the invention is illustrated by the accompanying drawings in which Fi v 5 with a ortlon of the cover removed, Figure 2 is ap amof the permanent U shapedmagnets with the coil and armature in position, Figure 3 is an inverted plan of the device with the cover removed and Figure 4 is a view of the armature as attached to the pivot bar and stylus holding member.

The device illustrated b is built up as a'four pole balance armature system, comprising two U-shaped permanent magnets B, B, olarized at their extremities and arrange with their poles adjacent and so as to form a rectangle having a short,

air gap between the poles, and a-central rectangul'ar opening. I In the central opening formed by the magivot bar supported in or re 1 is a side view of the device these drawings nets is arranged a coil T wound with insulated copper wire, the axis of the coil being arranged to pass through the centres of the air gaps, that is midway between the oles of the magnets. and in their central plane. 68 In the air gap and passing through the centre of the coil (T is also arranged an armature S, which is reduced in thickness at S S, 'where it extends beyond the coil into the air gaps K between the magnet poles, its ends being flush e0 gitlouter sides of the arms of the magnets The faces of the magnets B are bevelled as shown so as to concentrate-th flux.

" The extremities of the armature S are secured to light metal arms H H e'xtendin downwardly clear of the c'oil-T and secure at their lower-ends by screws U tothe ends of a square sectioned pivot bar G to the centre. of which is secured a stylus holder J pro- 70 vided with a stylus securing screw K.. The bar G; has a reduced central portion G, to clear the coil T and reduce the length of the arms'H and H I The parts are held together by bracing plates E and F by a top plate A of insulat mg material, two U-sliapedplates O, C, also of insulating material and of a similar sha e to the magnets B B. The adjacent ens of the U-shaped plates 0, C grip between them rubber sheaths M M All these parts are held together b screwed rods D provided with nuts D ,an which pass through holes D provided for them in the parts.

Distance washers, collars or nuts N are provided on the screwed rods D between the magnets. B, B and the top plate A, and pieces of damping rubber L are provlded between the magnets-B, B and the top plate A. 00

On the top plate A is fixed by screw 0 an adapter 0 for fixing the device on the tone arm of a gramophone or other. sound reproducing instrument. .1 I I The coil T is supported in poslt on in openings in the plates A, and'magne s B, B ply securing it in. the opening'm the plates G, 1 by means of waxo'r'other suitable material and the ends of ,tbe coil are secured to terminals P .13 to" which 'are also secured. the

sheaves of rub r M, M between the adja cent arms of the plates G, C, forms a heavily damped pivot so that the vibrations of the stylus such as produced by passing over a sound record are transmitted to the armature S and the efiect thereof is to produce alternating currents in the coil T'and these are transmitted by the leads Q), Q ato a thermionic valve'amplifier, and thereby operate any usual form 0 reproducer. Q

What I claim and desire to secure by Letters Patent. is

1. A device for transforming vibrations into an alternating'current comprising an armature, a current carrying coil, a permanent magnet, a vibrator, a pivot bar, and supporting means for holding the parts together, the armature being arranged to'extendthrough the coil while being supported from V the pivot bar with its opposite'ends extend-- ing. respectivel into the magnetic fields of both poles of t e magnet, the pivotbar also supportin'gthe vibrator.

2. A device for transforming vibrations into an alternating current comprising an armature, a current carrying coil, two permanent. horse shoe magnets, a vibrator, a

pivot bar and means for holding the parts together, the two magnets being supported opposite each-other in the same lane with air gaps between .their adj acent po es, the. arma ture be in arranged ,to extend through the 0011 with its opposite ends in. the air gaps between the magnets, such ends being supported from the opposite ends of the pivot bar, the pivot bar also supporting the vibrator.

the two arms of both magnets, and the two magnets supported opposite each other in the same plane with air gaps between their adjacent poles and the armature arranged to extend through the coil with its opposite ends in the air gaps between the magnets, and such ends supported from the opposite ends 7 of the pivot bar,-which pivot bar also sup:

the vibrator on the opposite side there- 4. A device for transforming vibrations 3. A device for transforming vibrations into an alternating current comprising an armature, a current carrying coil, a permanent magnet, a vibrator, a pivot bar, means for damping the pivot bar, and supporting means for holding the parts together in position, the armature being arranged to extend through the coil while being supported from the'pivot bar with its opposite ends extending respectively into the magnetic fields of both (poles of the m'agnet,the vibrator being supported by the bar, and the pivot bar supported at each end by the damping means therefor.

5. A device for transforming vibrations .into an alternating current, comprising an armature, a current carryirfgcoil, two permanent horse shoe magnets, a vibrator, a

pivot bar, sheet insulating material, and

means forholding the parts together, the two magnets being supported opposite each other in the same planewith air gaps between their adjacent poles, the armature being arranged to extend through the coil with its opposite ends in the air gaps between the magnets, such ends being supported from opposite ends of the pivot bar,'the pivot her also supporting the vibrator and being supported between the ends of -sheets of insulated.material which are arranged parallel to the magnets and secured thereto by the means for holding the arts together. 1 v p 6. A device or transforming vibrations into an alternating current, comprising an armature, a currentcarrying coil, two permanent horse shoe magnets, a vibrator,apivot bar, sheet insulating material and means for.

holding the parts together, the two magnets being .supported opposite each other in the same plane with air gaps between their adjacent poles, the armature being arranged to extend through the coil with its opposite ends in-the air gaps between-"the magnets, 'such endsbeing supported from'the opposite end of the pivot bar, the .pivotbar also supporting the vibratorandbeing supported between the ends of sheets of insulating material which are arranged parallel to the magnets and secured thereto by the means for holding the parts together, such means also holding sheet insulating material on the opposite side of the magnets.

7. A device for transforming vibrations into an alternating current, comprisingan armature, a curved carryingbcoil, a permanent magnet, a yibrator, a pivot A supporting arms, and supportingmeans for at, two armature holding the parts together, ,the armature ends of the armature supporting am being fixed on the respective ends of-the "pivot bar,

and the pivot bar also supporting the vibrator being arranged to extend through the coil so as to extend from the pivot bar in the opposite direction to the armature supporting arms.

{manent horse shoe magnets, a vibrator,a-

pivot bar having at opposite ends armature supporting arms, and means for holding the 1 pa-rts together, the two magnets being supported opposite each other in the same plane with air gaps between their adjacent poles, the armature being arranged to extend through a the coil and having its opposite ends flattened so as to extend into correspondingly shaped.

air gaps between the magnets, such endsbeing supported by the pivot bar arms, the pivot bar also supporting the vibrator on the opposite side to the armature supporting arms.

9. A device for transforming vibrations into an alternating current comprising an armature, a current carrying coil, two permanent horse shoe magnets, a vibrator, a pivot bar, sheet insulating material, a magnet damping rubber, and'means for holding I the parts together, the two magnets being supported opposite each other in the same plane with air gaps between their adjacent poles, the armature being arranged to'extend through the coil with its opposite ends in the air gaps between the magnets, such ends being supported from the opposite ends of the pivot bar, the pivot bar also supporting the vibrator and being supported between the ends of sheets of insulating material which are arranged parallel to the ma ets and secured thereto y the means for olding the parts together, such means also holding the sheet insulating material on the opposite side of the magnets with the magnet amp'ing rubber between it and the magnets when the damp Eng rubber is in a position extending acrossthe air gap between the magnets.

In witness whereof I aflix m si ature. LEONARD WALTER MEI! M.

8. A device for transforming vibrations i'ntoan alternating current, comprising an armature, a current carrying coil, two per- 

